Boat hoist

ABSTRACT

A boat hoist for launching a boat and for removing it from the water. This hoist includes a scissor-type extensible and retractable arm assembly connected at one end to a support platform for a boat. The entire supporting structure for the hoist is mounted upon the shore and the other end of the scissor assembly is operatively secured to the shore mounted support. The extension of the scissor assembly projects the boat platform over the water and to a prescribed depth therein and the retraction of the arms elevates the boat platform from the water towards the shore support where the boat can be maintained in a docked position free of the water.

[ 1 July 11,1972

United States Patent Osmundson 3,350,065 l0/l967 Mankey.... r....... ...........74/52l [54] BOAT HOIST [72] Inventor: air-:83; gblmms 400 Broadway, mman' ammimr -rrysve M mix Attorney-Morton S. Adler Oct. 22, 1970 [22] Filed:

ABSTRACT A boat hoist for launching a boat and for removing it from the water. This hoist includes a scissor-type extensible and retractable arm assembly connected at one end to a support platform for a boat. The entire supporting structure for the hoist is mounted upon the shore and the other end of the scissor assembly is operatively secured to the shore mounted support. The extension of the scissor assembly projects the boat platform over the water and to a prescribed depth therein and the retraction of the arms elevates the boat platform from the water towards the shore support where the boat can be maintained in a docked position free of the water.

8 Clubs, ll Drawing Figures 2 5| mmwn Mon 4 38 4 34 ah n W 3 u" M m m m Em 6 W31 m I 42 n u m m m I all 9 W m W JW W m m Wm w A m l P. n C B n m W T m m m H m m S m m m 6 PW& J "m" R 3 m T W 8 mm N 679 J u U 988 o m H l L C p a p s w 950 A h an ll H HUN m mm 2 555 5 [ii I PKTE'N'TEDJUL 1 1 1912 3. 675 258 sum 2 0F 11 IN MENTOR B24015! wMu/vwa/Y ATTORNEK SHEEI H 0F 4 IN VEN TOR. BAADL EY M. as/w/zvasaw ATTOPNEX w QM PATENTEDJUL 1 1 1972 son HOIST BACKGROUND OF THE INVENTION This invention relates to improvements in boat hoists of the type commonly found along the banks of rivers and lakes to facilitate the launching of boats and particularly to store them in a position completely out of the water when not in use.

Boat hoists of the general type indicated above are found in many varieties and are in common use particularly by those who have temporary or permanent residences on a river or lake. For such persons, their boat is usually kept at the water site for extended periods and when the boat is not in use, it is highly desirable that it can be clocked in such a way that it will not be subject to damage from wind or water as would be the case if it were tied to a fixed dock. For this purpose many forms of hoists are available which provide boat supporting platforms that can be lowered into the water and elevated therefrom. So far as can be determined, practically all such hoists have supporting structures that rest upon the bottom of the river or lake at suitable points relative to the bank and while such types of hoists will suitably support a boat and permit its launching into and removal from the water at times, it is necessary in areas where freezing temperatures occur to completely remove such hoists from the water during such cold season in order to prevent substantial damage thereto when the water freezes and subsequently thaws. The destructive effect of such freezing and thawing is well known and in climates where this occurs, not only must all boat hoists be removed from the water but likewise the annual removal and replacement of ordinary docks is a regular practice.

The disadvantages of present type boat hoists as referred to above and the expenses associated therewith have been completely eliminated by the present invention in which the principal object is to provide an improved boat hoist having its sole support on a shore mounted base and which is operable to support a boat whereby the boat can be extended into the water for launching and can be withdrawn out of the water for storage in a position completely free of any water contact.

A further object of the present invention is to provide a boat hoist of the above class which can be maintained in its operable position on a year round basis and is capable of supporting a boat at all times completely free of the water so that neither the hoist nor the boat if it is left thereon year round is subject to any damage from the freezing and thawing of the water and the movement of debris therein during such periods.

Still another object of the present invention is to provide a boat hoist as characterized which is relatively simple in construction and which may be suitably operated either manually or by power.

SUMMARY The present invention utilizes a support base or structure suitably mounted entirely upon the shore of a river or lake. Such structure includes a pair of vertically disposed and horizontally spaced tracks that may be anchored in concrete or in any other suitable manner. A pair of extensible and retractable scissor arms are disposed so that their respective end members move in a vertical plane and are mounted at one end to the respective tracks in such a manner that the lower ends of the scissor arms are pivotally secured thereto and the upper ends of such arms carry rollers disposed to move vertically therein. The other ends of the scissor arms are in a reverse arrangement to that at the shore support relative to a pair of spaced vertical tracks carrying a horizontal boat support platform so that on the tracks associated with the boat platform, the upper part of the scissor arms are pivotally secured thereto and the lower ends carry rollers.

Means for extending and retracting the scissor arms are provided at the shore support and this can be accomplished in a variety of ways by either manual or mechanical devices. For illustration, I have shown both cable and gear devices although it will be appreciated that other fon'ns may be used for the purposes involved.

The docking or out of the water position of the hoist normally maintains the boat approximately two feet out of the water which is satisfactory for general use during the boating season and likewise the boat platform is submerged approximately 2 feet for launching. Such dimensions, however, are not critical and can be varied as desired by the size of the scissor arms and number of scissor sections used. Preferably, the shore mounted support is vertically adjustable so it can be elevated an additional foot or more relative to the water level during a period of general non-use such as winter time as an added precaution for complete safety from shore line ice accumulations.

'The objects of this invention together with details of the operation outlined and the advantages of the same will be more fully described and developed in relation to the more detailed description of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of this new boat hoist showing the shore mounted base support and with the scissor arm assembly in partially extended position,

FIG. 2 is a side elevational view showing the hoist in retracted or elevated position with a boat on the boat supporting platform,

FIG. 3 is a side elevational view similar to FIG. 2 but showing the hoist in extended and lowered position with the boat in the water ready for launching,

FIG. 4 is a top plan view showing this hoist in extended position,

FIG. 5 is a cross sectional view taken on the line 55 of FIG. 2,

FIG. 6 is a fragmentary perspective view of the upper portion of the shore mounted support to illustrate a modified form for extending and retracting the scissor arms in relation to the shore mounted support,

FIG. 7 is a cross sectional view taken on the line 7-7 of FIG. 6,

FIG. 8 is a cross sectional view taken on the line 8-8 of FIG. 3 to show the movable attachment of the upper end of the scissor arms to the shore mounted support,

FIG. 9 is a sectional view taken on the line 99 of FIG. 8 to show the fixed pivotal connection of the lower scissor arm to the shore mounted support,

FIG. 10 is a front elevational view of the shore based track assembly to better illustrate its vertical adjustment relative to the shore oriented support base, and

FIG. II is a side view ofthe assembly in FIG. 10 showing the normal position in solid lines relative to water level and a selective elevated position in broken lines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, this new boat hoist is designated generally by the numeral 10 as best seen in FIG. I where it is shown in partially extended position and includes generally a shore mounted base or support 12, a boat supporting platform 14, an extensible and retractable scissor type arm apparatus 16 connecting the platform I4 to the base 12, and an operating mechanism 18 carried by the base I2 for effecting the extension and retraction of the boat platform I4 by means of the scissor apparatus 16. Such structure as briefly described and as will be referred to in detail as this description proceeds, is illustrated in its retracted position in FIG. 2 showing a boat 20 supported on platform 14 completely out of and above the surface of a body of water 22 and in FIG. 3, this hoist 10 is illustrated in its extended position where platform I4 is submerged in the water 22 so that the boat 20 may be easily floated or launched.

The base or supporting structure I2 includes the vertically disposed and horizontally spaced channel members 24 and 25 having the respective longitudinal slots 26 and 27 intermediate their ends. Such channel members are disposed so that the channel areas 28 and 30 as best seen in FIG. 6 are oppositely disposed to each other and define respective tracks or trackways as will later appear. The upper ends of channels 24 and 25 are connected by a beam 32. Support 12 as thus described is designed to be mounted securely by any suitable means upon the shore so that when it is so mounted, no part of the support will be in the water or resting on the lake or river bottom. It will be appreciated and understood that base 12 can be suitably and securely mounted at a shore location in a variety of ways and for purposes of the present disclosure, I have shown it mounted relative to a concrete seawall 34 although the use of a seawall is not a requirement for the present invention.

As best seen FIGS. 2 and 3, the seawall 34 presents a vertical face 36 at the shore line and, accordingly, I have anchored the channel members 24 and 25 to surface 36 of the seawall 34 by suitable anchor bolts 38 through slots 26 and 27. In addition I have provided diagonal braces 40 and 41 as best seen in FIG. 1 which are secured respectively at one end to the channels 24 and 25 through slots 26 and 27 by bolts 42 and are anchored at the other end into the seawall 34 as shown in FIG. 3. It will be noted that the lower end of channels 24 and 25 are spaced above the normal level of water 22 and when mounted as described, base 12 is securely anchored on a shore oriented support and, as indicated above, any other suitable means for anchoring base I2 in a similar location may be appropriately employed. In the normal use of this hoist 10, the platform 14 will be approximately two feet out of the water when retracted as seen in FIG. 2 and this has been found to be generally adequate during the general boating season. However, during the off-season when the boat is preferably in winter storage and shore line ice accumulations are possible, support 12 as best seen in FIGS. and 11 can be elevated an additional 18 to 24 inches by loosening the bolts 38 and 42 and using any suitable jack device for which an auto bumper jack is adequate and generally readily available. By tightening the volts with support 12 elevated it will be safe from damage over the winter and no dismantling or removal of the support relative to its shore mounting is required.

The boat platform 14 for purposes of reference includes an inner end 44 and an outer end 46. Platform I4 is substantially an elongated rectangular rigid frame structure including spaced parallel side pieces 48 and 50 connected at the inner end 44 by the cross member 52 and at the outer end 46 by the cross member 54 as best seen in FIG. 1. An intermediate cross member or support 56 connects rails 48 and 50 intermediate cross member 52 and approximately the longitudinal center of side pieces 48 and 50. Thus, cross pieces 54 and 56 serve to support the boat as will be obvious.

Secured to cross piece 52 in spaced relationship are the vertical channel members 58 and 60 which are connected at their upper ends by a cross member 62 corresponding in length and being parallel to member 52. Thus arranged, members 52 and 62 each project outwardly from the respective vertical planes of channels 58 and 60. The channel portions on members 58 and 60 are oppositely disposed to each other so as to provide the respective tracks or trackways 64 and 66 (FIG. 4) whereby the general construction and relationship of channels 58, 60 and member 62 provide a track containing frame assembly similar to that previously described for channels 24 and having the trackways 28 and 30.

As seen in FIG. 1, platform 14 includes the additional rails 68 and 70 which are secured respectively at one end to the respective end portions or rail 62 so as to extend on an incline toward the outer end 46 of platform 14 where they are secured in any suitable manner near the outer ends of rails 48 and 50. Intermediate their length, rails 68 and 70 are supported by appropriate braces 72 as shown. Thus arranged, rails 68 and 70 provide adequate support for end 54 of platform 14 and also serve as lateral guides for the boat 20 and as seen in F I68. 2 and 3 where the bow section of the boat will be protected from lateral movement relative to the supporting members ofplatform I4.

The scissor arm assembly I6 which, as indicated previously, connects the boat platform 14 to the base support 12, comprises a pair of parallel and connected scissor arms 74 and 76 as best seen in FIG. 4 which are of like construction so that only a description of arm 76 as seen in FIG 3 will be made and like parts on arm 74 will be given like numerals. The number of scissor type units in arm 76 is a matter of choice depending upon the distance of extension desired for platform 14 and the depth into the water in which it will move and for purposes of this application, as seen in FIG. 3, I have illustrated arm 76 by having three scissor sections, each of which includes an inner elongated rigid link 78 and an outer elongated rigid link 80 of like lengths which are pivotally connected at their center by pin 81. Each pair of links 78 and 80 constitute what I have referred to as a scissor unit and are disposed so that in the opening and closing of the scissor arms, the respective ends of such arms will move in a vertical plane. Thus at one extremity of arm 76 relative to the shore support 12 there is the respective upper end 82 and lower end 84 and at the opposite extremity, the corresponding ends are identified by the numerals 82' and 84'. The number of scissor units, as indicated above, will be a matter of choice and intermediate the end members 82 and 84 and 82' and 84, the respective ends of such intermediate scissor units on arms 74 and 76 are connected for pivotal movement in any suitable manner such as by the tu bu- Iar members 86. In this regard and with reference to FIG. 5, the inner scissor arms 78 are secured to the outer surface of tube 86 and made rigid by means of a gusset 88. The outer arms 80 are secured to respective sleeves 90 which are rotatably joumalled on the respective ends of tube 86. This has proved to be a satisfactory arrangement for the scissor arm action but it will be understood that any other suitable means for producing the scissor arm efiect may be used.

The lower ends 84 of scissor arms 74 and 76 are connected by a tubular member 92 as best seen in FIG. 9 and such ends 84 are pivotally attached by any suitable bearing means such as 94 to the lower portions of the shore mounted channel members 24 and 25 so that while such ends 84 will pivot rela' tive to such channels, they will not move vertically relative thereto. The upper ends 82 of scissor arms 74 and 76 are also connected by a tubular member 96 as best seen in FIG. 8 and the extremities of such tube are provided with appropriate roller members 98 which are vertically movably disposed within the trackways 28 and 30 in the respective channels 24 and 25. At the opposite ends of scissor arms 74 and 76, the reverse arrangement to that described is provided whereby the upper ends 82 are connected by the tube 100 as best seen in FIG. 1 and are pivotally arranged relative to the upper portion of rails 58 but not vertically movable relative thereto in the same relationship as for ends 84 on channels 24 and 25. The lower ends 84' of scissor arms 74 and 76 are suitably connected by an appropriate tube (not shown but similar to the tube 96 in FIG. 8) on which there are provided the rollers 102 (FIG. 3) which are rollably joumalled in the tracks 64 and 66 of channels 58 and 60 in the same manner as the arrangement of end 82 in tracks 28 and 30.

Thus far described, it will be seen in FIG. 2 when the scissor arms 16 are retracted that the vertical movable arm ends 82 are at their upper extremity of travel relative to the upper end of the shore support 12 and that the pivotally attached but not vertically movable arm ends 82' will be planar with ends 82. Also, in this position the roller arm ends 84' are disposed at the lowermost point of channels 64 and 66 at the inner end 44 of boat platform I4 and such arm ends 84' are planar with arm ends 84. As the scissor arms 16 are permitted to extend by means as will later be described, it will be seen in FIG. 3 that roller arm ends 82 move downwardly relative to the shore support 12 so that as the platform 14 is projected outwardly frame assembly 58, 60 and 62 with arm ends 82' attached thereto move downwardly correspondingly and with ends 82' remaining planar with arm ends 82. As this occurs, channels 64 and 66 ride downwardly over the roller ends 84 which remain planar with ends 84. It will thus be seen that while the scissor arm assembly remains on a horizontal plane during its extension, the top plane of such assembly is progressively lowered and by the reverse arrangement of roller ends 82 and 84', platform 14 is projected away from the shore line toward deeper water and lowered below the water level. When the scissor arms are retracted from the extended or launching position shown in FIG. 3 to that of FIG. 2 the reverse movements from those described take place. It will be appreciated that scissor arm ends 82 and 84' can be pivotally secured the same as ends 84 and 82 and while this could permit the extension and retraction of platform 14, hoist would of necessity have to be rather steeply tilted toward the relatively shallow water near the shore and would not have the advantage of my preferred embodiment described in projecting platform 14 during launching into deeper water more distant from the shore line.

It will be appreciated that various means and devices can be employed to effect the extension and retraction of this hoist arrangement and for purposes of illustration, l have shown the use of cable means together with an alternate gearing form illustrated in FIG. 6.

While it may appear from the description thus far that because of the normal weight of platform 14 and the scissor arm assemblies 16 and particularly if a boat 20 is on the platform, the arm assemblies would normally project to their extended position, experience has shown that with a sturdily constructed scissor arm assembly, a suitable manual or power means should be employed to facilitate the operation of such assembly. Accordingly, with reference now more particularly to FIGS. 1, 4 and I0, I provide an elongated shaft 104 disposed in parallel relationship above beam 32 and rotatably journalled in bearing members 106 and 108 so that such shaft projects outwardly relative to each bearing member. At one side of support 24, is secured a platform ill) to support a gear box 2 through which one end of shaft 104 is operatively arranged. Below shelf ll0 is a second shelf 114 on which is mounted a suitable electric motor 116 connected by a belt "8 to a large pulley wheel 120 mounted on a shaft 122 connected to the gear box 112 in a well known manner. A switch means 124 is suitably located and operatively connected to motor "6 in any well known manner. Wound in the same direction each projecting end portion of shaft R04 are the respective cables 126 and 128 that connect with the respective opposed end portions of the upper cross member 62 as best seen in FIG. 4. For this purpose, 1 preferably secure the ends of the respective cables 126 and 128 to the respective tumbuckles 130 and 132 which in turn are attached to the respective eyes 134 and 136 on rail 62. To keep such cables generally from lateral deflection, I provide the small compression springs 138 and 140 which connect the respective cables at their point of attachment to the tumbuckles to members 64 and 66. A third cable 142 is wound on shaft 104 intermediate cables 126 and 128 and in a reverse direction thereto and as best seen in FIG. 10 extends downwardly where it is reeved around a pulley 144 secured to tube 92 connecting ends 84 of the scissor arm assembly 16 and then extends upwardly where it is reeved around pulley 146 secured to tube 96 which connects ends 82 of assembly 16. From pulley 146, cable 142 extends downwardly where it is secured to an eye 148 on tube 92. By the above arrangement, it will be appreciated that with hoist 10 in retracted position as shown in FIG. 2, actuation of motor 116 to permit the proper directional rotation of shaft 104 for the unwinding of cables 126 and 128 and the winding of cable 142 results in tube 96 being pulled downwardly to correspondingly lower scissor arm ends 82 and 82' and permit the launching of boat 20 from the position shown in FIG. 3 as previously described. In this way, the extension of platform 14 and the retraction thereof is done under a controlled power arrangement so that there will be no damage to the boat. By reverse rotation of shaft 104, hoist 10 is returned to the position in FIG. 2.

in FIGS. 6 and 7, l have illustrated a modified form for controlling the extension and retraction of the scissor arm assembly l6 and this includes pivotally attaching to the cross beam 96' at end 82 a suitably threaded block 150 to receive an acme threaded shaft 152 operatively connected to a gear housing 154 mounted on cross beam 32. The gearing in housing 154 is shown arranged for manual operation by means of a handle [56 although it will be appreciated that this could be power operated, if desired. With this arrangement, it will be understood that operation of handle 156 will rotate shaft 152 and cause block 150 to move either upwardly or downwardly depending upon the direction of rotation. The effect of this will be the same as the operation of cables 126, 128 and 142. Accordingly, from all of the foregoing it is thought a full and complete understanding of this invention will be had and that the advantages of the same will be appreciated.

lclaim: l. A boat hoist, comprising: a support frame, means mounting said frame directly on the shore closely adjacent a body of water, an elongated boat support member disposed longitudinally over and above the body of water, said boat support member having respective inner and outer ends with said inner end being oriented in relatively close relationship to said support frame, an extensible and retractable arm assembly operatively secured at respective opposite ends to said support frame and to said inner end of said boat support member, means on said support frame operatively connected to said arm assembly to selectively effect the extension thereof away from the shore over and downwardly towards the water and the retraction thereof upwardly relative to the water and towards the shore and said support frame. the directional movements of said arm assembly relative to the water and shore effecting corresponding movements of said boat support member so that the extension of said arm assembly acts to project said boat support member in a direction away from the shore and into the water to a predetermined depth. and

the retraction of said arm assembly acts to elevate said boat support member and move it in a direction toward the shore to a predetermined plane above the level of the water adjacent the shore.

2. A boat hoist as defined in claim 1 including:

said support frame being vertically disposed, and

means attaching said support frame on the shore to permit of its vertical adjustment relative to the level of an adjacent body of water.

3. A boat hoist as defined in claim 1 including:

said arm assembly comprising:

a scissor arm unit including a pair of elongated rigid arms pivotally connected at their longitudinal center and having their opposite ends operatively connected respectively to said support frame and said boat support member.

4. A boat hoist as defined in claim 1 including: said arm assembly comprising:

a scissor arm unit including a pair of elongated rigid arms pivotally connected at their longitudinal center and having at each opposite extremity a pair of end members defining an upper end and a lower end which move in a substantially vertical plane during the extension and retraction of said scissor arm unit,

said lower end at one extremity of said arm unit being pivotally secured to said support frame at a point above water level and said upper end at the corresponding extremity being slidably arranged relative to said support frame above said lower end, and

said upper end at the other extremity of said arm unit being pivotally secured to said boat support member at a point above water level and said lower end at the corresponding extremity being slidably arranged relative to said boat support member below said upper end.

5. A boat hoist as defined in claim 4 including:

said means on said support frame to effect the extension and retraction of said arm assembly comprising:

a shaft mounted on said support frame for rotation about its longitudinal axis,

a source of power for rotating said shaft in two respective opposite directions,

a first cable means wound in one direction on said shalt and connected to said arm assembly adjacent said boat support member, and

a second cable means wound in the opposite direction on said shaft and operatively connected to said upper end of said arm assembly adjacent said support frame whereby in one direction of rotation of said shaft, said second cable pulls said upper end of said scissor arm unit downwardly relative to said support frame to effect the extension of said scissor arm during which time said first cable means unwinds and in the reverse rotation of said shaft. said first cable means winds up to effect the retraction of said scissor arm unit with said second cable means unwinding to permit said upper end to move upwardly relative to said support frame.

6. A boat hoist as defined in claim 4 including:

said means on said support frame to effect the extension and retraction of said am assembly comprising:

a block with a threaded bore having a vertical axis opera tively connected to said upper end of said scissor arm unit relative to said support frame,

a vertically disposed shaft on said support frame mounted for rotation about its longitudinal axis and threadably journalled in said block, and

means on said support frame associated with said shaft to selectively rotate the same in two respective opposite directions whereby in one direction of rotation said upper end of said scissor unit is moved downwardly to effect the extension of said arm assembly and rotation of said shaft in the opposite direction moves said upper end upwardly to effect the retraction of said arm assembly.

7. A boat hoist as defined in claim 1 including:

a vertically disposed first trackway on said support frame,

the lower end of said trackway being fixed at a point above the level of the water,

a second vertically disposed trackway carried by said boat support member,

said arm assembly comprising:

a scissor arrn unit including a pair of elongated rigid arms pivotally connected at their longitudinal center and having at each opposite extremity a pair of end members defining an upper end and a lower end which move in a substantially vertical plane during the extension and retraction of said scissor arm unit,

said lower end at one extremity of said scissor arm unit being pivotally secured to the lower end of said first trackway and said upper end at the corresponding extremity being slidably arranged relative to said trackway,

said upper end at the other extremity of said scissor arm unit being pivotally secured to the upper end of said second trackway and said lower end at the corresponding extremity being slidably arranged relative to said trackway,

the corresponding upper and lower ends of said scissor arm unit at respective opposite extremities being at all times planar with each other whereby with said arm assembly retracted, said upper end in said first trackway is at the upper end thereof and said lower end in said second trackway is at the lower end thereof and in the extension ofsaid arm assembly, said upper end in said first trackway slides downwardly therein to effect a corresponding lowering of said second trackway and boat support member at which time said second trackway slidably moves downwardly relative to said lower end of said scissor arm unit therein so that said boat support member is progressively projected away from the shore line and into the water. 8. A boat hoist as defined in claim 7 including:

means adjustably attaching said first trackway to said support frame to permit of its vertical adjustment thereon relative to the level of an adjacent body of water.

i i i i 

1. A boat hoist, comprising: a support frame, means mounting said frame directly on the shore closely adjacent a body of water, an elongated boat support member disposed longitudinally over and above the body of water, said boat support member having respective inner and outer ends with said inner end being oriented in relatively close relationship to said support frame, an extensible and retractable arm assembly operatively secured at respective opposite ends to said support frame and to said inner end of said boat support member, means on said support frame operatively connected to said arm assembly to selectively effect the extension thereof away from the shore over and downwardly towards the water and the retraction thereof upwardly relative to the water and towards the shore and said support frame, the directional movements of said arm assembly relative to the water and shore effecting corresponding movements of said boat support member so that the extension of said arm assembly acts to project said boat support member in a direction away from the shore and into tHe water to a predetermined depth, and the retraction of said arm assembly acts to elevate said boat support member and move it in a direction toward the shore to a predetermined plane above the level of the water adjacent the shore.
 2. A boat hoist as defined in claim 1 including: said support frame being vertically disposed, and means attaching said support frame on the shore to permit of its vertical adjustment relative to the level of an adjacent body of water.
 3. A boat hoist as defined in claim 1 including: said arm assembly comprising: a scissor arm unit including a pair of elongated rigid arms pivotally connected at their longitudinal center and having their opposite ends operatively connected respectively to said support frame and said boat support member.
 4. A boat hoist as defined in claim 1 including: said arm assembly comprising: a scissor arm unit including a pair of elongated rigid arms pivotally connected at their longitudinal center and having at each opposite extremity a pair of end members defining an upper end and a lower end which move in a substantially vertical plane during the extension and retraction of said scissor arm unit, said lower end at one extremity of said arm unit being pivotally secured to said support frame at a point above water level and said upper end at the corresponding extremity being slidably arranged relative to said support frame above said lower end, and said upper end at the other extremity of said arm unit being pivotally secured to said boat support member at a point above water level and said lower end at the corresponding extremity being slidably arranged relative to said boat support member below said upper end.
 5. A boat hoist as defined in claim 4 including: said means on said support frame to effect the extension and retraction of said arm assembly comprising: a shaft mounted on said support frame for rotation about its longitudinal axis, a source of power for rotating said shaft in two respective opposite directions, a first cable means wound in one direction on said shaft and connected to said arm assembly adjacent said boat support member, and a second cable means wound in the opposite direction on said shaft and operatively connected to said upper end of said arm assembly adjacent said support frame whereby in one direction of rotation of said shaft, said second cable pulls said upper end of said scissor arm unit downwardly relative to said support frame to effect the extension of said scissor arm during which time said first cable means unwinds and in the reverse rotation of said shaft, said first cable means winds up to effect the retraction of said scissor arm unit with said second cable means unwinding to permit said upper end to move upwardly relative to said support frame.
 6. A boat hoist as defined in claim 4 including: said means on said support frame to effect the extension and retraction of said arm assembly comprising: a block with a threaded bore having a vertical axis operatively connected to said upper end of said scissor arm unit relative to said support frame, a vertically disposed shaft on said support frame mounted for rotation about its longitudinal axis and threadably journalled in said block, and means on said support frame associated with said shaft to selectively rotate the same in two respective opposite directions whereby in one direction of rotation said upper end of said scissor unit is moved downwardly to effect the extension of said arm assembly and rotation of said shaft in the opposite direction moves said upper end upwardly to effect the retraction of said arm assembly.
 7. A boat hoist as defined in claim 1 including: a vertically disposed first trackway on said support frame, the lower end of said trackway being fixed at a point above the level of the water, a second vertically disposed trackway carried by said boat support member, said arm assEmbly comprising: a scissor arm unit including a pair of elongated rigid arms pivotally connected at their longitudinal center and having at each opposite extremity a pair of end members defining an upper end and a lower end which move in a substantially vertical plane during the extension and retraction of said scissor arm unit, said lower end at one extremity of said scissor arm unit being pivotally secured to the lower end of said first trackway and said upper end at the corresponding extremity being slidably arranged relative to said trackway, said upper end at the other extremity of said scissor arm unit being pivotally secured to the upper end of said second trackway and said lower end at the corresponding extremity being slidably arranged relative to said trackway, the corresponding upper and lower ends of said scissor arm unit at respective opposite extremities being at all times planar with each other whereby with said arm assembly retracted, said upper end in said first trackway is at the upper end thereof and said lower end in said second trackway is at the lower end thereof and in the extension of said arm assembly, said upper end in said first trackway slides downwardly therein to effect a corresponding lowering of said second trackway and boat support member at which time said second trackway slidably moves downwardly relative to said lower end of said scissor arm unit therein so that said boat support member is progressively projected away from the shore line and into the water.
 8. A boat hoist as defined in claim 7 including: means adjustably attaching said first trackway to said support frame to permit of its vertical adjustment thereon relative to the level of an adjacent body of water. 